This invention relates to a figure input system for time-wise continuously inputting coordinate data of basic figures such as line segments, triangles, rectangles, polygons, circles, ellipses and parabolas from a coordinate input device such as a digitizer or a tablet.
When it is desired to input an original figure into a computer, it has been customary to directly input coordinate data of figures by using a CAD (computer aided design) device such as a mouse, a digitizer or a tablet or, in the case of a word processor, keys, a mouse or a tablet with high pointing accuracy. On the other hand, the following two methods are known for inputting basic figures such as circles and rectangles into a computer. One is to use numeric keys or a light pen to input characteristic geometrical components of the basic figures such as the radius of a circle or the two sides of a rectangle and its position on the display screen such as the center of the circle or the center of gravity and the slope of the longer side of the rectangle. The other is to place a similar basic figure (having the same shape as the desired figure) at the desired position on the display screen by using numeric keys or a light pen and then to enlarge or reduce its size.
These prior art methods are designed to simplify the input by observing that basic figures are regularly shaped and hence can be uniquely determined if their characteristic geometrical data and positions are determined. Since basic figures are constituent elements of the final display, however, it is preferable that the user can directly draw a desired figure of a desired size at a desired position as by a conventional input method of original figures. From this point of view, the first of the two methods explained above is inconvenient because the positioning of the figure is effected indirectly and the second of them is inconvenient because the size of the desired figure is specified indirectly. By either method, the user's image cannot be fully reflected. These methods are therefore not easy to use. On the other hand, if basic figures are inputted in the same way as an original figure, it must be ascertained what kinds of basic figure are inputted by a digitizer or the like. In other words, sizes, orientations and so forth of many basic figures must be taken into consideration in comparing with an input figure and this becomes an enormous job. In addition, similarly shaped figures cannot be distinguished easily by such a method, for example, between a fan shape and an equilateral triangle having the same top angle.